Low temperature poly-silicon thin film transistors (TFT) have been widely used in various kinds of displays, such as Active Matrix Organic Light Emitting Diode, Active Matrix Liquid Crystal Display, and so on due to the advantages such as high mobility, stability, or the like.
A TFT used in the above-mentioned type of the display is generally prepared as follows. A layer of poly-silicon film is formed on a base substrate, and is patterned to form an active layer of the thin film transistor; a gate insulation layer is formed on the active layer; a gate electrode is formed on the gate insulation layer; then ions are implanted into the active layer to form a source electrode area and a drain electrode area, respectively; an interlayer dielectric layer is deposited to cover the gate electrode and the gate insulation layer; contact holes leading to the source electrode area and the drain electrode area are formed; and then a metal layer is formed and patterned to form a source electrode and a drain electrode electrically connected to the source electrode area and the drain electrode area through the contact holes, respectively. In the above manufacturing process for the TFT, dangling bonds having unbonded orbitals are generated at the interface between the poly-silicon film and the gate insulation layer, which is an important factor to increase the density of interface state at the grain boundary of the poly-silicon. Due to the influence of the dangling bonds, the display device is suffered from performance degradation, for example, the carrier mobility of the thin film transistor is reduced, and the threshold voltage is raised, and so on.
In order to provide hydrogen to the dangling bonds so as to make the dangling bonds passive at the interface between the poly-silicon film and the gate insulation layer, the most common hydrogenation method is conducted as follows: after the thin film transistor is completely formed, that is, after the metal layer is formed, performing anneal in hydrogen atmosphere to diffuse hydrogen to the gate insulation layer and the poly-silicon layer. Another common method is to use a silicon nitride film of the interlayer dielectric layer as the source of hydrogen and perform thermal treatment onto the thin film transistor.